[ASK] Hard Drive for web server

Hi, I'm new to server thingie.
I want to start a small web hosting business, but I really don't know what kind of HDD that I need for that kind of work.

- Let's assume I have about 10.000 registered users.
- I think mostly it would be read operation than write.
- my concern is affordability before perfomance or sweet spot between them. (remember this is new business, I'm not very sure to dump much money into this).

What HDD that I need? is 3.5" SATA enough? WD Velociraptor? or do I need SAS? or SSD? should it be RAID-ed?

lol, actually it's not like that.
as of now, I 'only' have few hundreds clients that using other company web hosting service.
then I think, why don't I start making my own web hosting service as complement to my own business.

so, usually one server (maybe dual Xeon or something like that) could only handle about 100-500 accounts?

and, which is better for that kind of job, SAS HDD (enterprise HDD?) or simple consumer grade SSD?